教程分析講稿mech-l01intro

1、Lesson content:IntroductionInteraction Options in AbaqusConnector Element BasicsConnector Applications and CapabilitiesConnectors vs. Multi-point ConstraintsFlexible and Rigid components in a ModelProceduresLesson 1: Mechanisms and Multibodies in Abaqus1 hourIntroduction (1/4)In this seminar, we con

2、sider rigid or flexible pieces that are attached by some type of discrete, point-to-point connection.In static or purely kinematic analysis, we often call such assemblies “mechanisms.” In transient dynamic analysis (especially with rigid bodies), we often call such assemblies “multibodies.”Introduct

3、ion (2/4)A wide variety of options exist for modeling the pieces that make up a mechanism or multibody, depending on the level of details included. For example,Every aspect could be modeled with deformable elements and all contact interactions defined at the connection points, etc. orEvery piece cou

4、ld be assumed rigid and all interactions between pieces idealized with node-to-node interactions.Such choices depend on what level of solution information you require from the analysis.Introduction (3/4)The connection is an idealization of the complex interaction between bodies.The complex interacti

5、on may include:kinematic constraints contact constraintsnonlinear spring or dashpot behaviorplastic behaviordamage mechanismfrictionlocking mechanismsdriven motionsinternal loadingIntroduction (4/4)Common examples of idealized connections in mechanisms or multibodies include:hingesshock absorbersuni

6、versal jointsconstant velocity jointsslidersweldsball-in-socket jointsplanar constraintspin-in-slot constraintshydraulic pistonsMany complex interactions can be viewed as combinations of basic connections used in parallel or series.The connections between parts in mechanisms and multibodies will be

7、the focus of this seminar.These connections are modeled with the 2-node elements called connectors or connector elements.Interaction Options in Abaqus (1/4)OverviewCreating a ponent or component-to-ground connection introduces constraints between partsThere are 3 ways to introduce constraints in an

8、FEA code:Degree of freedom elimination (eliminates constrained DOF)Penalty (springs between nodes) or augmented LagrangianLagrange multiplier (solve for the unknown constraint force)Abaqus uses all 3 methods depending on interconnection approachInteraction Options in Abaqus (2/4)Degree of freedom el

9、imination interconnections:Types:*BOUNDARY*EQUATION*MPC*KINEMATIC COUPLING*TIEAdvantages:Reduces the problem sizeDisadvantages:Eliminated DOFs cannot be used againOverconstraint is commonConstraint forces are not available as output (exception is *BOUNDARY)Interaction Options in Abaqus (3/4)Penalty

10、(spring) or augmented Lagrangian interconnections:Types:Interconnection elements (trusses, beams, etc.)Springs, dashpotsGasket elementsDefault friction model (penalty spring)Connectors in Abaqus/Explicit (Augmented Lagrangian)Advantages:Constraint output is availableNo problem with overconstraintsDi

11、sadvantages:Subject to ill-conditioning if spring constant is too highCan be noisy (in dynamic analysis)Interaction Options in Abaqus (4/4)Lagrange multiplier (solve for unknown constraint force) interconnections:Types:Default hard contactSoftened contactLagrange frictionDistributing coupling elemen

12、tsConnectors in Abaqus/StandardAdvantages:Exact Quadratic convergenceDOFs still availableConstraint force outputDisadvantages:DOFs are addedConnector Element Basics (1/3)Connector elements model discrete, physical connections between deformable or rigid bodies.Connector Element Basics (2/3)Connector

13、 elements are functionally defined by specifying the connector attributes:In the most general case, specify the following attributes:the connection types,the connector behaviors, andthe local directions associated with the connectors nodes.These attributes are associated with a set of connector elem

14、ents by specifying connector sections. Note: details on connector sections and behaviors will be discussed in Lectures 2, 6, and 7. Connector Element Basics (3/3)Connector elements can be actuated either through displacement or force controls. Examples include:Relative motion (displacement) actuatio

15、n, such as gear-driven deployment arms.The connector is given a known displacement, velocity, or acceleration history.Internal load (force) actuation, such as hydraulic pistons.The connector is driven by a known internal force or moment history.Note: details on connector actuation will be discussed

16、in Lecture 9.Connector Applications and Capabilities (1/7)Typical applications of connector elementsConnector elements can be used in many applications with flexible or rigid parts. Common applications include:Kinematic constraints; e.g., slot or revolute constraint.Oriented spring, dashpot, and fri

17、ctional behavior; e.g., torsional springs. Unidirectional contact conditions (GAP elements); e.g., “joint stops.”Less common but useful applications include:Solution-dependent locking conditions; e.g., falling-pin mechanism.Solution-dependent failure: e.g., release one or all local components of rel

18、ative motion based on constraint forces or local displacements.Boundary conditions in local (rotating) coordinate systems. Connector Applications and Capabilities (2/7)Connector elements add a wide variety of possible application areas to Abaqus. For example,vehicle durabilitycrash test dummiesdynam

19、ics of space structuresmachinery designkinematicslong-term dynamics of rigid systemssuspension modelsConnector Applications and Capabilities (3/7)Some of the capabilities that are unique to connectors:Complex attachments of rigid bodies at points other than the reference node (note that this can als

20、o be plished with spring elements).Torsional springs that rotate with the deformation.Constraint force and moment output.Complex finite rotation parameterizations that model physical mechanisms.Easy definition of nonstandard kinematic constraints.Rotational contact (inequality constraints on rotatio

21、nal degrees of freedom).Motion and load actuation of element local degrees of freedom.Boundary conditions and output in local, rotating coordinate systems.Connector Applications and Capabilities (4/7)Example: Simplified model of a loader-backhoeAXIAL and HINGE connectors are usedMechanism is driven

22、by displacement controlled actuation of connectors.Note: connectors can connect to points on a rigid body other than the rigid body reference point.RPConnector Applications and Capabilities (5/7)Example: Simplified model of a cylinder-cam mechanismSLOT-ALIGN, CARTESIAN and BEAM connectors are used.M

23、echanism is driven by cylinder rotation.Rotational motion is transformed into translational motion.Connector Applications and Capabilities (6/7)Connector elements as fasteners Allow for very complex behavior to be modeled with fasteners:The connection can be fully rigid or may allow for unconstraine

24、d relative motion in local connector components. Deformable behavior can be specified using a connector behavior definition which includes elasticity, damping, plasticity, damage, and friction. Example: Rail crush with rigid fasteners using BEAM connectorsConnector elementsDeformable fasteners still

25、 holdingFailed fastenerFailed fastenersDeformable fastener still holdingConnector Applications and Capabilities (7/7)Example: Rail crush with deformable fastenersThe rail flanges now are connected using fasteners that allow for plasticity, damage, and failure.Connectors vs. Multi-point Constraints (

26、1/4)Advantages of connector elements over multi-point constraints:Output of constraint forces and moments is available.Since connectors do not eliminate dependent degrees of freedom, they can be used in many situations where multi-point constraints cannot be used.For example: connectors can be used

27、between rigid bodies and there are no “chaining” restrictions.Connectors have a lot of functionality that is not available with MPCs (material behavior, actuation, etc.).Visualization is available with connectors.Connectors vs. Multi-point Constraints (2/4)Disadvantages of connector elements over mu

28、lti-point constraints:Since connectors do not eliminate degrees of freedom, the analysis is more expensive.Connectors generally have only 2 nodes, whereas there are MPCs with more than 2 nodes.MPCs have some functionality not available with connectors.For example: Mesh refinement MPCs.Connectors vs.

29、 Multi-point Constraints (3/4)Some connections duplicate the names and functionality of MPCs.MPC typeConnectorREVOLUTEREVOLUTEUNIVERSALUNIVERSALLINKLINKBEAMBEAMConnectors vs. Multi-point Constraints (4/4)Some connections have similar, but not identical, functionality and different names of MPCs.The

30、difference in the name comes from the difference in the constraint formulation. They are slightly different constraints: Connection types JOIN and WELD operate on nodal total displacements/rotations.MPCs PIN and TIE operate on the incremental displacements/rotations.Some connections are particular f

31、or connector elements, such as BUSHING, FLOW-CONVERTER, and SLIPRING. MPC typeConnectorPINJOINTIEWELDFlexible and Rigid Components in a Model (1/5)Components in a model can be:Flexible (Modeled using deformable elements)Rigid (Modeled using rigid bodies or display bodies) Flexible componentsThe defo

32、rmation of the component is taken into accountAllow for the study of stresses at a component-levelRigid componentsAssume components will not deform (has only 6 DOFs)Allow for the study of kinematics and dynamics of the modelFaster computational timeFlexible and Rigid Components in a Model (2/5)Defin

33、ing rigid bodies in Abaqus Rigid bodies are common in mechanisms or multibody analysis.Used for visualization, proper geometry for attachment points, automatic calculation of mass properties, using same model for deformable and rigid analysis, etc.Rigid bodies are easily defined.A rigid body is a co

34、llection of nodes, elements, and/or surfaces whose motion is governed by the motion of a single node, called the rigid body reference node.Flexible and Rigid Components in a Model (3/5)Usage*RIGID BODY, REF NODE=n, ELSET=, ANALYTICAL SURFACE=, PIN NSET=, TIE NSET=Keywords InterfaceAbaqus/CAE Interfa

35、cedouble-clickFlexible and Rigid Components in a Model (4/5)Defining display bodies in Abaqus If a component is rigid, it can be modeled by rigid links: Mechanisms and multibodies created from connectors and rigid links are often sufficient for predictive resultsBut it is not easy to visualize the r

36、esultsDisplay bodies can be used for visualization purposes:No meshing required for part geometries (a display body constraint is applied to a part in Abaqus/CAE)Display bodies are ignored during the analysis faster analysis time than when using rigid bodiesTips:Use rigid bodies if the component may

37、 be used as deformable in a subsequent analysis.Use display body to speed up the analysis.Flexible and Rigid Components in a Model (5/5)Deformable elements, rigid bodies, and display bodies can be used together in an Abaqus model. Mixed Flexible and Rigid Bodies Display BodiesProcedures (1/5)Connect

38、or elements are valid for all procedure types in Abaqus. They are most commonly used with the following types of analysis procedures:Explicit dynamics.Small and large deformation implicit analyses (static and dynamic).Linear perturbation analyses with Abaqus/Standard (such as frequency extraction, e

39、igenvalue buckling, etc.)Procedures (2/5)Use in geometrically linear analysesIf a connector element with a nonlinear kinematic constraint is used in a geometrically linear analysis, the kinematic constraint is linearized.Example: Consider the LINK connection type in a geometrically linear analysis.

40、Assume that node a is fixed and node b should occupy the position indicated by b” under the applied load.In a linear analysis, however, node b assumes the position indicated by b and always stays on the red dotted line.Initial positiondeformed position with NLGEOM=Yesdeformed position with NLGEOM=Noabbb”LINKProcedures (3/5)Use in geometrically linear analyses (contd)Thus, the distance between the two nodes in the LINK connector element, when projected onto the original configuration, is held constant.It is strongly